Marijuana use may lead to a significantly higher risk of contracting COVID-19 despite being fully vaccinated, according to the results of a new study.
The study was published Tuesday in the journal World Psychiatry and focused on COVID-19 “breakthrough” infections in fully vaccinated people diagnosed with substance use disorder (SUD), a condition that involves uncontrolled dependence on substances including marijuana, alcohol, cocaine, opioids and tobacco. While breakthrough infections were seen in 3.6 percent of vaccinated people without SUD, the study found that 7 percent of those with SUD had breakthrough infections.
At 7.8 percent, the risk of breakthrough infections was highest among those with marijuana use disorder. For every other type of substance, the apparently increased risk of contracting COVID-19 after being fully vaccinated disappeared when researchers accounted for factors like underlying health conditions, housing difficulties or economic hardships. The study speculated that the increased risk that remained in those using marijuana could be due to behavioral differences or the effects that the drug has on lungs or the immune system.
“Patients with cannabis use disorder, who were younger and had less comorbidities than the other SUD subtypes, had higher risk for breakthrough infection even after they were matched for adverse socioeconomic determinants of health and comorbid medical conditions with non-SUD patients,” the researchers wrote. “Additional variables, such as behavioral factors or adverse effects of cannabis on pulmonary and immune function, could contribute to the higher risk for breakthrough infection in this group.”
The study also found that those who received the Pfizer/BioNTech vaccine were at a greater risk of breakthrough infection than those who received the Moderna vaccine—findings that are in line with other research that has suggested the Moderna vaccine offers more protection against highly contagious Delta variant. Antibodies that protect against the virus are also believed to diminish in Pfizer recipients faster than in those who received the Moderna vaccine.
The study was led by researchers at the National Institute on Drug Abuse (NIDA), which is part of the National Institutes of Health. It is not clear that the conclusions of the study apply to casual or medical marijuana users, as it was narrowly focused on those with SUD. The researchers noted that, despite the apparently increased risk of breakthrough infections, the overall rate of infection in fully vaccinated people with SUD was still low when compared to the unvaccinated.
“First and foremost, vaccination is highly effective for people with substance use disorders, and the overall risk of COVID-19 among vaccinated people with substance use disorders is very low,” NIDA Director Dr. Nora D. Volkow, one of the study’s lead authors, said in a statement. “We must continue to encourage and facilitate COVID-19 vaccination among people with substance use disorders, while also acknowledging that even after vaccination, this group is at an increased risk and should continue to take protective measures against COVID-19.”
Newsweek reached out to the National Cannabis Industry Association for comment.